Shading on model is not smooth in some places
What you're most likely experiencing is cycles not being able to shade properly on such a lowpoly mesh.

Some things that could fix this are:


Adding a Subsurf modifier to your mesh can smooth it out and remove some artifacting.
Having Auto Smooth in Data &gt;&gt; Normals unticked or set to 180 can remove unwanted sharp edges.
Increasing the size of you sun lamp also smooths out the shading.